Such a gas-operated firearm is known by the name of Sauer 303. It also contains a system box or a lock housing, a guide rod that projects forward, as seen in the shooting direction, and a lock activation device, which is arranged so it can be displaced on the guide rod and which interacts with a lock for its movement between a locking position and an unlocking position. A barrel with a gas withdrawal block is affixed to the lock housing. It contains at least one gas withdrawal borehole that opens into the barrel and a pressure piston that is guided so it can be displaced axially in the gas withdrawal block, for displacement of the lock activation device against the force of a lock spring. In this known gas-operated firearm, the rear end of the barrel is inserted into a corresponding holder borehole of the lock housing and it is firmly connected by a connecting piece, in the area of the gas withdrawal block, with the front end of the guide rod. For the installation or dismantling of the barrel, the front shaft must first be removed in this known gas-operated firearm and then the connection between the barrel and the guide rod must be loosened, before the barrel can be pulled out from the holder borehole of the lock housing.
With other known gas-operated firearms, the front shaft must always first be dismantled if the barrel is to be removed.